Fuel cells have recently attracted attention as clean energy sources. Among these fuel cells, solid oxide fuel cells (hereinafter referred to as “SOFCs”) using solid ceramic materials as electrolytes are expected to be used in a wide variety of applications ranging from domestic power supplies to large-scale power generation, due to their advantages such as high operating temperatures allowing utilization of waste heat and high efficiency power generation.
As a SOFC, a stack of single cells each including an electrolyte sheet and electrodes provided on the electrolyte sheet is used. The long-term stability of the power generation performance of the SOFC requires sophisticated quality control of each electrolyte sheet.
One of the important parameters for the quality control of electrolyte sheets is a so-called “burr”, which is, for example, a change in the height of the surface of the peripheral portion of a sheet. If burrs are present on the peripheral portion of a sheet, they may cause defects such as cracking in the sheet during printing of an electrode or even poor printing of the electrode, resulting in uneven formation of the electrode or susceptibility to delamination thereof. Furthermore, a SOFC is composed of a stack of series-connected single cells each including an electrolyte sheet and electrodes. Therefore, during the stacking of the single cells or the power generation of the SOFC, stresses are concentrated on the burrs on the peripheral portion of the electrolyte sheet, which may cause fracture of the electrolyte sheet.
Thus, various techniques focusing on burrs on the peripheral portion of an electrolyte sheet for a SOFC have been developed. For example, Patent Literature 1 proposes, for use as an electrolyte sheet a SOFC, a ceramic sheet having a reduced burr height of 100 μm or less on its peripheral portion.